This invention relates to an improved method for manufacture of printing plates, such as offset printing plates, by use of photo mechanical plate making techniques. More particularly, this invention relates to a method for manufacture of printing plates used to simultaneously print a multiple number of pages associated with a signature. The invention further relates to a method for preparing a photographic negative from which the printing plates are made. The invention thus constitutes an efficient manner to more quickly and more easily arrange and make such photographic negatives used in the manufacture of printing plates.
A multiple page printed sheet having a predetermined number of pages arranged in serial order after folding the sheet is known as a signature. Before the sheet is folded it is known as the signature sheet.
Typically, the opposite sides of printed signature sheet are printed with multiple pages of copy. There may, for example, be anywhere from 2 to 64 pages on each side of a signature sheet depending, for example, upon the size of the page. Each printed signature sheet is then cut and folded in an appropriate manner to provide signatures which may be bound together to form the book or magazine. The particular geometrical arrangement of a printed signature sheet for each size signature can be determined and is well known to those skilled in the art depending upon the printing process, the size of the page, the size of the signature and the number of signatures; for example, see pages 97-104 of "Pocket Pal--a graphic arts production hand book", Thirteenth Edition, May 1983, International Paper Company.
In order to make printing plates that are used to prepare a printed signature sheet for a multiple page signature, various plate making techniques may be used particularly with respect to lithographic printing, gravure printing, and letter press printing. To make printing plates using photo mechanical plate making techniques, it is necessary to initially prepare a photographic negative or films which may be used in the plate making apparatus for the manufacture of the printing plate. Thus, film is prepared which replicates all or a portion of one side of a sheet for the signature. The film, in turn, is used to prepare a printing plate using some type of photo mechanical technique.
As a first step when preparing the film, it is necessary to prepare a layout of each page of the copy. The layout is then photographed. For example, when preparing a four page signature, each page of copy may be individually photographed. The photograph or film for each page is then trimmed and properly arranged on a backing or support known as a signature mounting sheet. Alternatively, a number of pages of copy may be simultaneously photographed. The pages are then separately cut from the film and the film for each page is trimmed and properly positioned on a signature mounting sheet also known as a masking sheet.
A great deal of effort and time is necessary in order to properly trim and align the pages of film on the signature mounting sheet or masking sheet. Any changes or modifications of the film copy must be made on the signature mounting sheet. Ultimately, a composite negative film is made or formed by the artisan. That film contains an image of all of the pages necessary to make a printing plate used for printing one side of a signature sheet.
Thus, after the negative or film is, in effect, put together on the signature mounting sheet by a skilled artisan, it may then be placed in the plate making machine to create a printing plate by photo mechanical procedures. A need remains, therefore, to devise a method by which a signature negative or film can be prepared without requiring assembly of a composite negative or film on a signature mounting sheet.